Oscillator



f u circuits.

Patented Feb. 27, 1934 OSCILLATOR Joseph G. Beard, Springfield, Mass., assignor to Westinghouse Electric & Manufacturing Company, a corporation of Pennsylvania Application October 21, 1931 Serial No. 570,1991/2 8 Claims.

My invention relates to crystal-controlled oscillators and particularly to oscillator of the type employing a three-electrode crystal holder.

A common form of crystal controlled oscillator in use at the present time is one which employs a two-electrode crystal holder. When operated at low frequencies (at frequencies below 300 kilocycles, for example), this form of oscillator has several undesirable features. One of these features is that the crystal must be carefully selected or it will not oscillate. In fact, below a certain frequency it is impossible to make any crystal oscillate in the two-electrode holder circuit, when using only one vacuum type in conventional Another undesirable feature of the twoelectrode holder circuit is that it will not start oscillating at a low-frequency with even the best of crystals unless the vacuum tube filament is heated slowly and then the plate voltage applied to the tube, or unless the plate voltage is applied slowly and then the filament heated.

By means of my invention I provide a crystalcontrolled oscillator which does not have the above-mentioned objectional features. My improved oscillator is of the general type described in Cady patent, Reissue No. 17,246, granted March 26, 1929, it being an oscillator having a three-electrode crystal holder so connected that the frequency of the oscillator is determined by the constants of the crystals. It has been found, however, that when the apparatus is connected as shown in the Cady patent, the oscillator rrequires a more critical adjustment than is desirable.

An oscillator constructed in accordance with my invention is easily adjusted. It operates as satisfactorily at high frequencies as at low frequencies. 'I'o change from low frequency operation to high frequency operation, it is only necessary to switch to a holder containing a high frequency crystal and to replace the grid leak resistor by a resistor having a suitable lower value, Thus, my invention provides an oscillator which may be operated by crystal control over an unusually Wide frequency band. When employing my oscillator for high frequency operation the amplitude of the crystal oscillations can be controlled readily by varying the value of the grid leak resistor. For such operation the resistor is preferably made variable.

An object of my invention is to provide an oscillator of the above-mentioned type which even inexperienced operators may set into oscillation at low frequencies without difliculty.

(Cl. Z50-36) A further object of my invention is to provide a. crystal-controlled oscillator of the threeelectrode type which may be readily adjusted to operate at the desired frequency and which cannot be thrown out of adjustment easily.

A still further object of my invention is to pro- Y vide a crystal-controlled oscillator which may be operated over a wide band of frequencies.

In practicing my invention, I employ a thermionic amplifier having an anode circuit which includes either an inductance coil alone or an inductance coil tuned by means of a variable condenser.

A three-electrode crystal holder having one small electrode is connected in the circuit with the small electrode connected to the anode. knected between the grid and filament.

A grid leak of the proper value is con- Other features and advantages of my invention will appear from the following description taken in connection with the accompanying drawing, in which in Fig. 2.

Referring to Fig. 1, the oscillator comprises a thermionic amplifier tube having a control electrode 10, an anode 11 and a filament 12.

tery 13 or other source of potential for the anode A bat- 11 has its negative terminal connected to the cathode l2 and its positive terminal connected to the lower end of an inductance coil 14 through a switch 15.

The upper end of the inductance coil 14 is connected to the anode 11 through a switch 16.

The battery is shunted by a by-pass condenser 17 having a low impedance at radio frequencies.

The inductance coil 14 may be replaced by a resistor, but it has been found that the output of the oscillator is greater if the inductance coil is employed. In some cases, it is desirable to replace the inductance coil 14 by an inductance coil 18 tuned by means of a variable condenser 19, as illustrated. By means of switches 15 and 16 either the inductance coil 14 or the tuned circuit may be connected into the anode circuit.

A piezo-electric crystal 20, preferably a quartz crystal, is mounted in a crystal holder having a lower electrode 2l which is connected to the filament l2, a large ring-shape electrode 22 con-I trode 22 and connected to the anode 11.

In Some cases it may be desirable to connect the electrode 23 to the anode 11 through a condenser. If the condenser is variable it may be employed to control the amplitude of the crystal oscillations.

It has been found that the operation of the oscillator is more satisfactory if the plate is connected to the center electrode 23 instead of to the ring electrode 22. Probably the reason for this is that the plate connection to the smaller electrode 23 introduces only a small controllable amount of feed-back and also that the capacity shunted across the choke coil 14 or tuned circuit 18, 19 by the crystal holder is kept small.

A grid leak resistor 24 is connected between the grid 10 and the negative side of the filament 12.

'I'he three-electrode crystal holder, which is employed in the circuit described above, is shown in detail in Figs. 2 and 3. The holder comprises a heavy circular metal block 2l having three holes 31 therein which are screw-threaded. This block forms the lower electrode 21 which is connected to the filament 12, and it is of larger area than the side of the crystal contiguous to it.

Two electrodes 22 and 23 are spaced away from the lower electrode 21 by means of quartz washers 32. The electrodes 22 and 23 are assembled as a unit, the small disc-shape electrode 23 being positioned in the center of the ring-shape electrode 22 and being insulated therefrom and clamped in position by means of insulating bushings 33, washers 34 and nuts 35. The electrodes at both faces of the crystal 20 overlap the peripheral edge of the latter.

The ring-shape electrode 22 is fastened to the lower electrode by means of screws 36 and is insulated therefrom by means of the insulating bushings 37 and washers 32. A spring washer 38 positioned between a plain washer 39 and the head of the screw 36 holds the electrode 22 firmly in place.

Pins 40 which extend through the electrode 21, are provided to hold the quartz crystal 20 in position, it being understood that the crystals 20 is positioned loosely between these pins.

In one example of my invention a UX210 tube was employed, the rated voltage of 7.5 volts being applied to the ilarnent and 200 volts being applied to the plate. The grid leak had a resistance of 8000 ohms when the choke coil 14 was connected into the plate circuit and a resistance of 2000 ohms when the tuned circuit 18, 19 was employed. With these values, the circuit would immediately stop oscillating if a connection to any one of the crystal-holder electrodes was roken.

In the above described example, the crystal was a Y-cut quartz slab having a natural frequency of 1000 kc., the circuit oscillating at this frequency X-cut crystals may be employed but, as they are less active than Y-cut crystals, the resistance of the grid leak should be increased.

The coil la is radio-frequency choke coil having a resonant frequency above the frequency of the crystal.

Tlvhen the tuned circuit 1S, 19 is substituted for the coil 14, the circuit 18, 19 is so tuned that it is resonant at a frequency higher than the natural frequency of the crystal.

rlhe diameter of the electrode 21 in the above described example was 21% inches. The other dimensions be determined from the drawing as it is drawn to scale. The dimensions of the crystal holder are of importance only in that the grid leak resistance and other circuit values must be changed if the crystal holder dimensions are changed. rlhe important feature of the circuit adjustment is that if any one of the three connections to the crystal holder is broken the tube will not oscillate.

Assuming the crystal-holder dimensions and circuit constants, with the exception of the grid leak resistance, are the saine as given above, the following grid leak resistances have been found satisfactory; at a frequency of 150 kilocycles-a grid leak resistance of 15000 ohms; at a frequency of 250 iro-a grid leak resistance of 10,000 ohms; at a frequency between 500 kc. and 1000 kc.-a grid leal: resistance of 7000 ohms; at a frequency between 1000 kc. and 1500 kc.-a grid leak resistance of 1000 ohms. In an oscillator in which the choke coil was replaced by the tuned circuit, the oscillator functioned properly between 1000 kc. and 2000 kc. with a grid leak resistance of 2000 ohms.

Various modifications may be made in my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art and are set forth in the appended claims.

I claim as my invention:

1. An oscillator comprising a tube having a cathode, an anode, and a control electrode, a voltage source and an impedance element connected between said cathode and said anode, a piezoelectric crystal, an electrode on one side thereof, two electrodes on the other side thereof, one of said two electrodes being substantially smaller piezo-electric crystal, an electrode on one side of said crystal connected to said cathode, two electrodes on the other side of said crystal, one of said two electrodes being in the shape of a ring and the other of said two electrodes being positioned within the ring and being of smaller area than said ring, said ring-shape electrode and said other electrode being connected to said control electrode and to said anode, respectively.

3. A crystal-controlled oscillator comprising a tube having a cathode, an anode, and a control v electrode, a voltage source and an inductance coil connected between said cathode and said anode, a grid leak resistor connected between said control electrode and said cathode, and a threeelectrode crystal holder comprising an electrode connected to said cathode, and two electrodes facing said first electrode, one of said two electrodes being substantially smaller in area than the other and being connected to said anode, and the other of said two electrodes being connected to said control electrode.

4. A crystal-controlled oscillator comprising a tube having a cathode, an anode, and a control electrode, a voltage source and a tunable resonant circuit connected between said cathode and said anode, a grid leak resistor connected between said control electrode and said cathode, and a threeelectrode crystal holder comprising an electrode connected to said cathode, and two electrodes facing said first electrode, one of said two electrodes being substantially smaller in area than the other and being connected to said anode, and the other of said two electrodes being connected to said control electrode.

5. An oscillator comprising an amplifier including a cathode and having an input circuit including a grid and an output circuit including an anode, an electro-mechanical vibrator having two electrodes of substantially different area, the smaller of said two electrodes being connected to said anode and the other being connected to said grid, said electro-mechanical vibrator having a third electrode opposite said two electrodes which is connected to said cathode, said vibrator being adapted to vibrate mechanically when stimulated electrically and to respond electrically when vibrated mechanically.

6. A piezo-electric crystal holder comprising a first electrode, a ring electrode, means for holding said ring electrode spaced away and insulated from said first electrode, a third electrode centrally positioned with respect to said ring electrode, and means for holding said third electrode spaced away and insulated from said other electrodes.

7. A piezo-electric crystal holder comprising a first electrode, a ring electrode, means for holding said ring electrode spaced away and insulated from said first electrode, a third electrode centrally positioned with respect to said ring electrode and having a smaller area than said ring electrode, and means for holding said third electrode spaced away and insulated from said other electrodes.

8. A piezo-electric crystal holder comprising a first electrode, a second electrode having a hole therein, means forholding said second electrode spaced away and insulated from said rst electrode, a third electrode positioned within said hole, and means for supporting said third electrode from said second electrode and for insulating it therefrom.

JOSEPH G. BEARD.

DISCLAIMER 1,948,692.J0scph G. Beard, Springfield, Mass. OsCILLAToR. Patent dated February 27, 1934. Disclaimer iiled March 26, 1935, by the assignee, Westinghouse Electric c@ Manufacturing Company.

Hereby enters this disclaimer to claim 6 of the above patent when modified by substituting the term enclosing for the term ring, and claim 8 of the patent, except when the enclosing electrode and third electrode of claim 6, and the second and third electrodes of claim 8 are oi unequal areas.

The claims in question are in the following words, to wit:

6 as modified. A piezo-electric crystal holder comprising a irst electrode, an enclosing electrode, means for holding said enclosing electrode spaced away and insulated irom said irst electrode, a third electrode centrally positioned with respect to said enclosing elect-rode, and means for holding said third electrode spaced away and insulated from said other electrodes.7

S. A piezo-electric crystal holder comprising a first electrode, a second electrode having a hole therein, means for holding said second electrode spaced away and insu- -lated from said first electrode, a third electrode positioned within said hole, and means lor supporting said third electrode from said second electrode and for insulating it therefrom.

[Oct'al Gazette, April 16, 1935.]

DISOLAI MER l,948,692.-Joseph G. Beard, Springield, Mass. OscILLAToR. Patent dated February 27, 1934. Disclaimer iiled March 26, 1935, by the assignee, Westinghouse Electric c@ Manufacturing Company.

Hereby enters this disclaimer to claim 6 of the `above patent when modified by substituting the term enclosing7 for the term ring, and claim 8 of the patent, except when the enclosing electrode and third electrode of claim 6, and the second and third electrodes of claim 8 are of unequal areas.

The claims in question are in the following words, to wit:

6 as modified. A piezo-electric crystal holder comprising a first electrode, an enclosing electrode, means for holding said enclosing electrode spaced away and insulated from said first electrode, a third electrode centrally positioned with respect to said enclosing electrode, and means for holding said third electrode spaced away and insulated from said other electrodes.

8. A piezo-electric crystal holder comprising a first electrode, a second electrode having a hole therein, means for holding said second electrode spaced away and insulated from said first electrode, a third electrode positioned Within said hole, and means for supporting said third electrode from said second electrode and for insulating it therefrom.

[Oficial Gazette, April 16, 1935.] 

